1. Field of the Invention:
The present invention relates to the improved microencapsulation of compounds by interfacial polyaddition, and, more especially, to the preparation of microcapsules, the wall members of which are comprised of polyurea.
2. Description of the Prior Art:
Published French Patent Application No. 85-18,453, filed Dec. 10, 1985, describes a process of microencapsulation by interfacial polyaddition, by emulsifying, in an essentially aqueous liquid, a hydrophobic organic liquid containing a polyisocyanate and, if desired, a dissolved organic material, and then forming the walls of the microcapsules by adding a polyamine, such process being characterized in that the polyisocyanate comprises:
(i) an aliphatic diisocyanate; and
(ii) the isocyanurate ring trimer of an aliphatic diisocyanate, in a diisocyanate/trimer weight ratio of 0.05/1 to 0.70/1.
The isocyanurate ring trimer may be the trimer of the aliphatic diisocyanate employed or the trimer of another aliphatic diisocyanate.
Representative aliphatic diisocyanates which may be employed are, for example, 1,6-diisocyanatohexane, 1,5-diisocyanato-2-methylpentane, 1,5-diisocyanato-3methylpentane, 1,4-diisocyanato-2,3-dimethylbutane, 2-ethyl-1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,4diisocyanatobutane, 1,3-diisocyanatopropane, 1,10-diisocyanatodecane, 1,2-diisocyanatocyclohexane, 1,4 -diisocyanatocyclohexane, 1,2-bis(isocyanatomethyl) cyclobutane, bis(4-isocyanatocyclohexyl)methane and 3,3,5-trimethyl-5-isocyanatomethyl-1-isocyanatocyclohexane.
The isocyanurate ring trimers of these aliphatic diisocyanates are prepared in a manner which is known per se. For example, they may be prepared by heating in the presence of a catalyst such as a tertiary amine, a phosphine or an alkali or alkaline earth metal oxide, hydroxide or carboxylate. These catalysts are described in Journal of Cellular Plastics, January 1965, pages 85 to 90, or in Macromolecular Chemistry, (5/1) pages 103 to 109 (1970).
French Patent Application No. 81/02,192 (published under No. 2,499,085) describes a process for preparing these compounds containing an isocyanurate group by cyclotrimerization of aliphatic isocyanates, catalyzed by a substituted disilazane.
And French Patent Application No. 81/23,135 (published under No. 2,517,674) describes a process which is identical to that noted immediately above, catalyzed by a compound containing an aminosilyl group.
The aliphatic diisocyanate/trimer weight ratio preferably ranges from 0.10/1 to 0.45/1.